Control of Blood Vessels: Peripheral Resistance Flashcards

1
Q

What does the blood vessel radius depend on

A

active tension exerted by smooth muscle (vascular smooth muscle)
passive elastic properties of wall (elastin and collagen)
blood pressure inside vessel
(tissue pressure outside vessel - veins)

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2
Q

What is the law of laplace?

A

distending pressure = wall tension / radius

where pressure = intra - extravascular pressure

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3
Q

What maintains vessel calibre?

A

distending pressure and Tw (wall tension)

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4
Q

Rearrange equation for distending pressure to find wall tension and radius

A

Tw = P x r

r = Tw / P

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5
Q

Compare wall tension between small and large vessels and why?

A

smaller in small vessels

increase in radius increases wall tension

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6
Q

What may occur if distending pressure is too high?

A

vessel rupture

>1000mmHg

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7
Q

How do blood vessels resist increasing pressure?

A

elastic tissue develops tension passively in response to a rise in pressure to confer stability
adish

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8
Q

What can smooth muscle develop?

A

active tension, which is independent of distending pressure

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9
Q

What does active control of vessel calibre allow?

A

redistribution of blood flow
control of pre/post capillary sphincters
regulation of vascular tone and control of blood pressure

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10
Q

What is vascular tone?

A

degree of constriction/dilatation

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11
Q

In vasoconstriction what tension is acting?

A

increased active tension

decreased passive tension

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12
Q

In vasodilatation, what tension is acting?

A

decreased active tension

increased passive tension

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13
Q

Which vessels does vasomotor tone describe?

A

arterioles and arteries

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14
Q

Which vessels does venomotor tone describe?

A

venules and vein

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15
Q

What factors affect vascular smooth muscle contraction?

A
nerves
hormones
endothelium-derived vasorelaxants
endothelium-derived vasoconstrictors
metabolites
myogenic mechanisms
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16
Q

What other NTs may cause vasocontriction?

A

ATP and NPY

tend to work with NA

17
Q

How do nerves affect vascular smooth muscle?

A

noradrenaline released from sympathetic nerve varicosity
binds to α2 and α1 on SM - vasoconstriction
binds to β2 - vasodilation
primarily activates α1 adrenoceptors in most vascular beds

18
Q

How do hormones affect vascular smooth muscle?

A

Catecholamines -
eg. noradrenaline, adrenaline (constrict/dilate)

Peptides - eg. vasopressin, angiotensin (constrict)
bradykinin (dilate)

19
Q

Which endothelium-derived vasorelaxants affect vascular smooth muscle?

A

PGI2 - prostacyclin
NO - nitric oxide
EDHF - endothelium-derived hyperpolarising factor

20
Q

Which endothelium-derived vasoconstrictants affect vascular smooth muscle?

A

endothelin

21
Q

How do metabolites affect vascular smooth muscle?

A

increase lactate, increase H+, released K+, generation of adenosine from breakdown of ATP - vasodilatation

systemic circulation - high O2, low CO2 - localised constriction
pulmonary vasculature - high O2, low CO2 - dilatation

VICE VERSA

22
Q

Where is myogenic mechanisms important?

A

important in cerebral vasculature

and kidney

23
Q

Why are myogenic mechanisms important?

A

important contributer to autoregulation of blood flow

24
Q

How do myogenic mechanisms affect vascular smooth muscle? (autoregulation of blood flow)

A

increased pressure is sensed, arteries stretch causing vasoconstriction
offsets increased flow (due to increased pressure) by increasing resistance

25
What are extrinsic control mechanisms primarily concerned with?
regulation of arterial BP
26
How does this autoregulatory range help predict pathologies?
if increase in pressure exceeds certain value, vessels cannot contract enough - risk of stroke pressure decreases too much, too much dilatation - risk of unconsciousness and ischaemic damage
27
What differs between different vascular beds?
``` function differs can behave differentially depending on the situation ```